Probable vaginismus

I am 17, I have been with the same sexual partner (my boyfriend) for 2 and a half years. Pretty much every time we've ever had sex (penetration specifically), it goes perfectly fine the first time he goes in, but then the second time he enters it always burns (pretty badly). If he keeps going then it stops hurting after a little bit.
At first we thought it was a lubrication problem (and I was told by my first gynecologist it was), but it turned out it still burned even with extra lube. A few times it's been so bad he only touches the entrance and it burns very badly. I have heard this could be a condition called vaginismus, where the pelvic muscles contract involuntarily. I looked up treatments and I found kits, but they're expensive, and it seemed to me those kits are for women who have this condition very severely.
I want to know if there is an easy (or not expensive) way to treat this. What is frustrating about this is that it is not enough of a big problem that I want to spend lots of money on it, at least compared to the other health issues and medications I spend my emotional and physical energy on. Not to mention all of the money my parents spend on those other issues.